Galium constrictum or Galium palustre?

Galium constrictum or Galium palustre? - UK and Ireland : This is id on vegetative state only as none of them were flowering.
Found in very species rich SSSI wet grassland amongst rushes, sedges and near to marsh marigold. Wet all year round, but particularly so in the winter. The ground gets very poached by

This is id on vegetative state only as none of them were flowering.

Found in very species rich SSSI wet grassland amongst rushes, sedges and near to marsh marigold. Wet all year round, but particularly so in the winter. The ground gets very poached by cattle in the winter and provides a mosaic of high and low niches. The bedstraw was found on the high (slightly drier in the summer) clumps and in the wet all year round depressions. The height of the largest plant was 25cm but most were about 16cm tall. The stem is square, just under 1mm in diameter and had small downward facing spines restricted to a single row on each corner of the square only visible through a hand lens. The leaves were arranged in whorls of four (90%), occasionally in whorls of five (8%) and rarely in whorls of 6 (2%). The leaves ranged in length between 4.5mm and 7.5mm and ranged in width between 0.8mm and 1.75mm. The leaves ended in an abrupt point but not mucronate. The leaf upper and lower surface glabrous. Margins not revolute. The spines on the leaves were facing forwards towards the tip of the leaf and backwards towards the stem but 75% of the spines were perpendicular to the margin. When the stem was snapped, a vascular bundle was in the centre of the stem.

I am aware that G. constrictum is restricted to the south of England which is why I am asking for advice. According to the land owner, 20+ years ago a botanical survey was done on the SSSI and the botanist found 'a small white flower that only occurs in a couple of locations in the UK'. Could this be it? or does the search continue?